Finding the Fourth Proportional to 42.65, 58.78 and 39.91

Step by Step Solution

1. Step 1: Write the proportion equation
   42.65 : 58.78 = 39.91 : x
2. Step 2: Convert to fraction form
   42.65/58.78 = 39.91/x
3. Step 3: Cross multiply
   42.65x = 58.78 × 39.91
4. Step 4: Simplify right side
   42.65x = 2,345.42
5. Step 5: Solve for x
   x = 2,345.42/42.65
6. Step 6: Final answer
   x = 54.99